The present invention is directed toward ion-sensitive or triggerable, water-dispersible or water-soluble cationic polymers, and more particularly to a method of making such cationic polymers.
It has been proposed that ion-triggerable cationic polymers be used as a binder for fibrous webs in the manufacture of disposable products such as diapers, wet wipes, incontinent garments and feminine care products. It has been discovered that such ion-triggerable cationic polymers have adequate in-use strength to bind different fibrous layers of disposable products together, but will readily dissolve or disintegrate in water providing the ability to dispose of the product by flushing it down a toilet, if desired. The polymer has a “trigger property” meaning that the polymer is insoluble in monovalent and/or divalent salt solutions at concentrations above about 0.3% by weight, but is soluble when the solution is diluted with water, such as when the product is discarded into water contained in a toilet. This allows the fibrous web to break apart and disperse enabling the product to be flushable.
Ion-sensitive polymers comprised of acrylic acid and alkyl or aryl acrylates are disclosed in U.S. Pat. No. 5,312,883, U.S. Pat. No. 5,317,063 and U.S. Pat. No. 5,384,189. The ion-triggerable polymers disclosed in these patents are acrylic acid-based terpolymers, which comprise partially neutralized acrylic acid, butyl acrylate and 2-ethylhexyl acrylate. The disclosed terpolymers, however, are limited in their application as a flushable binder material to geographical areas having soft water rather than hard water because these terpolymers fail to adequately disperse in water containing more than about 15 parts per million Ca2+ and/or Mg2+ ions.
In U.S. Pat. No. 6,423,804 there is disclosed a modification of the acrylic acid terpolymers of the above-referenced '883, '063 and '189 patents. More specifically, the '804 patent discloses a sulfonate anion modified acrylic acid terpolymer which has improved dispersability in relatively hard water, as compared to the unmodified terpolymers of the above-referenced patents. The sulfonate modified terpolymer of the '804 patent is prepared from four monomers, namely, acrylic acid, a sulfonate containing monomer such as 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), or the sodium salt thereof (NaAMPS), butyl acrylate and 2-ethylhexyl acrylate. These four monomers are dissolved in an acetone/water mixture. The monomer solution is deoxygenated, and the monomer solution along with an initiator dissolved in acetone are then added together and polymerized. Distillation removes the excess acetone and deionized water is then added to reduce the viscosity of the polymer solution.
Although numerous solution polymerization techniques are known, there remains a need for providing a method of preparing ion-triggerable cationic polymers because the anionic acrylic acid based ion-sensitive polymers and the sulfonate anion modified acrylic acid terpolymers of the above-referenced patents, when used as binders for personal care products, such as wet wipes, typically have reduced initial sheet wettability, increased dry sheet stiffness, increased sheet stickiness, reduced binder sprayability and relatively high product cost. Preferably, the process should desirably result in high yield of the polymer, be relatively economical, and be scaleable up to a commercial basis. In addition, the process must provide a cationic polymer having relatively high molecular weight because high molecular weight provides the strength necessary for use as a fibrous web binder. Finally, the process should be environmentally friendly, i.e. it should preferably not use any hazardous air pollutant (HAP) and/or any volatile organic compound (VOC) which might contribute to air pollution.